The present invention relates to a ball end mill for the chipforming machining of metal workpieces. The end mill comprises a tool body that is rotatable about its longitudinal axis. The forward end of the tool body is hemispherically shaped and has several separate pockets for the receipt of indexable inserts. One of the inserts is substantially triangular in shape and is mounted tangentially in the mantle surface of the tool body close to its center such that the main cutting edge of the insert is oriented generally radially and has one of its corner portions located at the center of the tool body. The invention furthermore relates to a polygonal throw away insert specifically designed for use with such an end mill.
Such ball nose end mills with indexable inserts are previously known, for instance as disclosed in U.S. Pat. No. 4,252,480. That ball nose end mill includes a central insert having a cutting edge of convex shape along a portion of the periphery of one of its side surfaces for the purpose of reducing the thrust forces. A basically similar ball end mill with throw away inserts is known from U.S. Pat. No. 4,618,296 in which all inserts have a generally triangular shape and are tangentially oriented in the tool body. The convex formation is achieved by making the outermost surface of the insert partially convex in shape.
It has been discovered, however, that the cutting forces acting on each insert of the above-described known ball end mills become high and are unfavorably distributed over the tool body. Further, each insert must be active during a long cutting engagement in the workpiece. It would, therefore, be desirable to provide a ball end mill with several inserts that are mounted in an optimal fashion over the mantle surface of the end mill so that a more limited portion of the cutting insert corner comes into engagement with the workpiece at different engagements.
With this background in mind, it is an object of the present invention to provide a ball nose end mill in which a more optimal and even distribution of the cutting forces acting on the inserts is achieved while providing for good chip removal at each insert.